| A ramjet engine has multiple flow modes during operation. The nonlinearity ofcombustor-inlet interactions leads to complex hysteresis in flow mode transitions,and this makes engine active control more difficult. In this article, the researchobject is an internal compression ramjet engine. First, based on the physical modeland assumptions presented, models of multiple flow modes are described.Considering the essential nonlinearity and the dominant system dynamics, anonlinear dynamic model of flow mode transitions responding to changes in heataddition ratio is developed, including duct volume effect, upstream acoustic wavepropagation and equilibrium manifold linearization model for shock dynamic.Second, flow mode transitions are classified based on the Kantrowitz theory.And simulations for flow mode transitions are performed under different incomingflow and geometric structure size conditions, using the dynamic model developed.The multistability of the system is analysed through the simulation results.Hysteresis modes of flow mode transition indicate combustor-inlet interactions.Guided by the thought of classification, hysteresis functions of flow modetransitions are discreted based on the geometric attribute, and a5layer classificationis obtained with the basis of classification proposed. Combined with the dynamicanalyses on flow mode transitions in Chapter3, mathematical models of the5layerclassification criterions are developed respectively. In addition, the distributioncharacters of multiple hysteresis modes and all kinds of critical hysteresis mode areanalysed.At last, since the mode-nested structure of flow mode transitions, we present ahierarchical control method for restart control, the upper for hysteresis mode leveland the lower for flow mode level. Simulations for hierarchical restart control areperformed, based on the dynamic model developed. |
